The present invention relates to a head for a high pressure homogeniser for the treatment of products with solids and fibres, comprising:                a block defining a passage for the products from an intake area to a delivery area;        a piston, movable axially in reciprocating motion within the block to pump the products in said passage, from the intake area to the delivery area;        intake and delivery valves positioned internally to the body and operatively active on said passage to open it/close it as a function of a motion of the products in the passage.        
The present invention pertains to the technical sector of high pressure homogenizers or piston pumps for the treatment of products. In particular, the present invention relates to high pressure homogenizers and piston pumps for the treatment of products containing particles, agglomerates or fibres, i.e. substantially liquid products, but subject to the formation of solid portions (e.g., said particles, agglomerates or fibres) during the treatment. It should be noted that products of this kind are also called “shear-sensitive”; in particular, to said type belong products that polymerize by effect of the mechanical stress applied to them during pumping/homogenization.
With regard to high pressure homogenization and pumping, known technical solutions entail the use of heads of the type described below.
A head according to said known technical solutions comprises a block defining in its interior a passage for the products, from an intake area to a delivery area. Within the body is movable a plunging piston. Said piston moves with reciprocating rectilinear motion to pump the products in the passage, from the intake area to the delivery area. In particular, the piston slides in its own seat obtained within the block and interfering with said passage. The piston is movable between an outer dead centre and an inner dead centre, whereat the piston reverses the direction of its motion. The outer dead centre corresponds to the position in which the piston is inserted in the block to the greater extent, whilst the inner dead centre corresponds to the position in which the piston is inserted in the block to the lesser extent (i.e. more retracted relative to the block itself).
Generally, the head comprises a plurality of pistons (e.g. three pistons), connected to a crankshaft, operating in parallel to each other, i.e. actuated by the shaft in such a way that its own reciprocating motions are appropriately offset from each other by an angle of 360°/n where n is the number of pumping pistons.
In this case, the block defines in its own interior, for each piston, a passage for the products, said passage intersecting the area (i.e. the seat defined by the block) in is which the piston moves during its reciprocating motion, according to the travel of the piston. Therefore, each piston, in its motion, interferes with a corresponding passage. In particular, when the piston in its inner dead centre, the passage is substantially free, whereas when the piston is in the outer dead centre, the passage is interrupted, i.e. at least partially occluded, because the piston is inserted within the passage, i.e. the cylinder in which the motion of the piston occurs intersects the pseudo-cylindrical hole having as its axis the axes of the valve assembly. More specifically, during the motion of the piston interfering with the passage, the product substantially flows in an inter-space (or jacket) defined between the piston and the seat in which the piston itself moves.
Therefore, the motion of the piston has the effect of subjecting the products to a strong compression and shear stress, this entailing the formation of filaments, particles, agglomerates or fibres (with the possible polymerization of the product) or of causing its accumulation in the restricted passage areas.
The head also comprises delivery and intake valves, active on the products to enable or prevent the passage according to a motion of the products. In particular, each of said valves comprises a ball connected to a spring and slidably associated to a guide. In the solutions with a plurality of pistons and passages, the head further comprises an intake manifold and a delivery manifold, in which end the passages, so that the intake manifold feeds the products to the various passages (upstream of the action of the pistons) and the delivery manifold receives the products from the same passages (downstream of the action of the pistons). Each valve is positioned at the confluence between a corresponding manifold and the passage whereon it is active.
In this light, the high pressure homogenization or pumping of said products containing elements/portions in solid phase with a head of the known type has some problems.
Said products, within a standard head, tend to accumulate the solid phase dispersed or being formed by effect of the stresses generated by the machine (in particular, by the piston) on the product; said accumulation ultimately prevents the proper operation of the pump or of the homogenizer, blocking in fact the automatic operation of the intake and delivery valves, thereby preventing the pumping of the product.
In particular, through its own research and testing activity, the Applicant has identified some critical areas within the head, corresponding to a particularly high probability of formation or accumulation of said solid portions of the products.
Such critical areas, with reference to the head described above of a known homogenizer, are indicated below.
A first critical area is constituted by the pumping valves, i.e. by the intake and delivery valves, because they are apt to promote the accumulation of said solid portions of the products (fibres, filaments, etc.).
In particular, the spring represents an area of accumulation of solid residues of the products that ultimately prevent the correct axial movement of the ball, hence preventing the opening and closing movement of the valve and consequently the functionality of the machine, which can be restored only disassembling the head and its components for manual cleaning.
A second critical area is constituted by the piston pumping in reciprocating motion relative to its own seat, in particular because of the presence of said inter-spaces which constituted forced passages, with limited cross section, for the products. Moreover, the fact that the motion of the piston in the displacement between the outer dead centre and the inner dead centre and vice versa interferes with said passage, partially obstructing it, prevents the passage of any agglomerates of the product, thereby contributing to create the conditions of generation of solid agglomerates in polymerizing products by effect of the stresses applied to the products.
A third critical area is constituted by the delivery manifold, where to an axial flow of the product coming from the (delivery) valve is associated a tangential flow that impacts on the upper area of the valve, causing an additional accumulation of solid and polymerized parts, especially in the area of the spring and of the valve guide; this effect contributes to the poor operation of the valve and consequently of the homogenizer itself.
Therefore, known homogenizers have various drawbacks, when they are used to process such types of products, and in fact they typically get stopped due to failure or malfunction a short time after processing starts.
FR-A-1252884, which is considered to be the closest prior art, discloses a high pressure homogeniser which does not have a straight passage free of obstacles positioned in the block in position of non-interference with the motion of the piston. Other conventional homogenizing apparatus are known from U.S. Pat. No. 2,901,981 and U.S. Pat. No. 4,773,833.